Range Of Tip Speed Ratios Research Articles

Experimental Optimization of the SG6043 Airfoil for Horizontal Axis Wind Turbines Using Schmitz Equations

This study presents the experimental optimization of the SG6043 airfoil for horizontal axis wind turbines (HAWTs) using the Schmitz equation, focusing on enhancing power output and elucidating the surface flow structure. Two blade models, M1 (conventional) and M2 (optimized), were designed and tested at rotational speeds of 400 rpm and 600 rpm across a range of tip speed ratios (TSR). The M2 model, optimized using Schmitz equations, demonstrated significantly improved performance compared to the M1 model at both rotational speeds. At 400 rpm, the maximum power coefficient (CP) for M1 was 0.274, while M2 reached 0.419, indicating a 52.91% improvement. At 600 rpm, M1 achieved a maximum CP of 0.293, whereas M2 attained 0.458, representing a 56.31% enhancement. The M2 model also showed superior performance at higher TSRs, with the highest percentage increase in CP recorded at 4.9 TSR, reaching 574.54%. Additionally, dynamic surface oil-flow visualization experiments were conducted to examine flow behavior on the blade surfaces. Results indicated better flow attachment in the M2 blade due to its optimized twist angle and chord length, particularly in the mid-section, leading to delayed flow separation. The reattachment observed on the suction side of the M2 model, following the laminar separation bubble (LSB), which was absent in the M1, contributed to its higher aerodynamic efficiency and overall power performance. These findings confirm that the optimized SG6043 airfoil design, guided by Schmitz equations, offers significant improvements in HAWT performance, particularly under varying operational conditions.

Drag reduction of lift-type Vertical axis wind turbine with slit modified Gurney flap

This study examines aerodynamic performance enhancement of Vertical Axis Wind Turbine (VAWT) blades with Gurney flap (GF) modified by slits. A quasi-3D computational fluid dynamics solution based on Reynolds-averaged Navier-Stokes model is employed to evaluate the effectiveness of slit GF blades, in particular the lift-to-drag ratio. The computational domain includes three pairs of GFs and slits combination along the blade span-wise direction to allow quasi-3D flow development while applying translational periodic boundary condition on the two end-wall boundaries. The inlet velocity is 9 m/s for a VAWT configuration with Tip Speed Ratios (TSRs) of 1.44, 2.64, and 3.3, respectively and each of these TSRs represents low, medium, and high regimes of TSRs. Simulation results have shown a significant 8% drag reduction for blades with slit GFs at medium range of TSRs, albeit with a 2% decrease in lift compared to blades with clean GFs. This improves the lift-to-drag ratio and enhances moment production. The power generation also shows increases of 1.5%, 6.5%, and 11.3% at low, medium, and high TSR regimes, respectively, for the analysed slit GF blades. The drag reduction is primarily attributed to the generation of small-scale vortices by the slit, dissipating large coherent flow structures more rapidly in the near wake-field.

Effects of the influence of triangular dimple and aspect ratio on NACA 4412 airfoil on the overall performance of H-Darrieus wind rotor: An experimental investigation

This study examines how adjusting aspect ratio (AR) and adding triangular dimples to the airfoil can enhance H-type Darrieus wind rotor (H-rotor) performance under low wind speeds (4, 6, and 8 m/s) using wind tunnel testing. Results show optimal performance at an AR of 1.0 for both standard and Triangular dimple airfoil H-rotors, with variations at different wind speeds for other aspect ratios. Triangular dimple-equipped H-rotors demonstrate improved self-starting capability and a wider operational range of tip speed ratio (TSR) compared to standard rotors, ensuring reliability across diverse wind conditions. Moreover, the triangular dimple rotor achieves a nearly 13.6% increase in maximum coefficient of power ([Formula: see text]) compared to the dimple-free H-rotor at 4 m/s wind speed. This study underscores the efficacy of adjusting AR and integrating triangular dimple blades to enhance H-rotor performance, particularly in low wind speeds.

Effect of baffles on efficiency of darrieus vertical axis wind turbines equipped with J-type blades

This study investigates the effects of incorporating baffles in J-type bladed vertical axis wind turbines. The objectives are to analyze the behavior of vortices and their impact on turbine performance and to explore various locations for placing the baffles along the J-type blades. The 3D numerical simulations of the current study applies the sliding mesh techniques to better model the rotational motion of blades about the turbine axis with respect to the wind. The results show that mounting zero-thickness baffles over the tips of the blades effectively reduces vortex leakage, minimizes tip vortices, and increases the pressure differential across the sides of J-type blades leading to a significant improvement of the turbine performance. At low tip speed ratios (TSRs) of 0.5, 0.75 and 1, in particular, the torque generation in comparison with conventional NACA0021 straight bladed turbines has been improved by up to 49.5 %, 38.2 %, and 28 %, respectively. Considering a wide range of TSRs, on average, the implementation of baffles results in a 17.5 % increase in torque generation. The effect of the baffle thickness on generated vortices and their evolution along the course of flow is also investigated to show how the zero-thickness baffles improves the blade aerodynamics.

Experimental investigation into the effects of endplate designs for a Savonius turbine

Abstract Wind energy is experiencing a trend of exponential growth in both literature and industrial employment, emphasizing its current pivotal role in achieving carbon neutrality by replacing fossil fuels. Vertical axis wind turbines (VAWTs) particularly Savonius rotors operate at a lower tip-speed-ratio (TSR) range compared to horizontal axis wind turbines (HAWTs). The Savonius rotor has good starting characteristics, making it suitable to be placed in urban areas with lower wind speeds. Due to its low efficiency, studies on augmentation and optimization have been conducted to improve its blade and deflector designs. Extensive research has established a common consensus that the use of endplates significantly improves the aerodynamic performance of the Savonius rotor. However, limited research has been undertaken to explore the endplate design further. In this study, wind tunnel tests were conducted on different endplate ratios, to investigate the effects of endplate design on the aerodynamic performance of a conventional Savonius turbine. Three different Savonius rotor with no endplate, semi-circular endplate and circular endplate were designed and manufactured. Experiments were conducted in an open-type suction wind tunnel at a constant measured wind velocity of 5.89 m/s. The turbine’s performance for different endplate ratios was evaluated across a TSR range of 0.2 to 1.0. The performance was assessed based on the maximum power generated and its self-starting ability. From the experimental results, the circular endplate ratio of 1.1 shows a significantly high coefficient of power compared to both semi-circular and without endplates. This is due to reduced spanwise spillage and enhanced airflow capture by the rotor. The endplates direct incoming air to the advancing blade and overlap region, resulting in the increased pressure difference between the concave and convex sides of both the advancing and returning blade, thereby improving the power efficiency of the turbine with 1.1D diameter endplate and semi-circular endplate by 296.6% and 6.9% compared to no endplates case.

An Experimental Performance Assessment of a Passively Controlled Wind Turbine Blade Concept: Part A—Isotropic Materials

This paper is the first part of a two-part series, which presents preliminary findings on a novel flexible curved wind turbine blade designed for passive control, comparing its aerodynamic performance and behavior against a conventional straight blade. Characterized by its ability to twist around its longitudinal axis under bending loads, the flexible curved blade is engineered to self-regulate in response to varying wind speeds, optimizing power output and enhancing operational safety. This design utilizes inherent elasticity and specific geometric configurations to develop torsional loads, resulting in continuous adjustment of the blade’s pitch angle via twist–bend deformation. The study focuses on a comparative analysis conducted in a wind tunnel, testing both a small-scale model of the conventional blade and the flexible curved blade of equivalent diameter. Results indicate that the flexible curved blade concept successfully moderates its rotational speed and power output at higher wind speeds and demonstrates the capability to start generating power at lower wind speeds and stabilize power effectively, aligning with sustainability goals by potentially reducing reliance on active control systems. Despite promising outcomes, passive control mechanisms did not activate at the designed wind speeds, revealing a misalignment between expected and actual performance and underscoring the need for further refinements in blade design and control settings. Additionally, the power coefficient (Cp) versus tip speed ratio (TSR) comparison showed that flexible curved blades operate within a lower TSR range and exhibit controlled capping of power under high wind conditions, marked by a distinctive ‘hook-like’ feature in Cp behavior. This study confirms the feasibility of designing and manufacturing passively controlled wind turbine blades tailored to specific performance criteria and underscores the potential of such technology. Future work, to be detailed in a subsequent paper, will explore further optimizations and the use of Glass Fiber-Reinforced Polymer (GFPR) composite materials to enhance blade flexibility and performance.

A blind test on wind turbine wake modelling based on wind tunnel experiments: Phase I – The benchmark case

Wind turbine wake and modelling is crucial to optimizing future wind farm layouts and hence reducing the cost of energy. This paper presents the first phase of a blind test on modelling controlled and uncontrolled wind turbine wakes. The blind test is based on wind tunnel experiments of two model scale wind turbines (D = 1.1 m) one downstream of the other. The exercise is split into two phases and the first one is presented here, where participants are invited to simulate the baseline case, in which both turbines are aligned with the flow and there is no control on the either turbine. The objective of this phase is to ensure all participants can benchmark their numerical approach against a baseline open data set, where no wake control is applied. Experimental measurements include inflow velocity, turbine power and loads for a range of tip speed ratios. In the second phase, not presented here, the wake of the upstream turbine will be controlled and the performance of the downstream one will be recorded. This will be a blind test with the data not released prior to submissions. The present paper gives an overview of the initial, open benchmark case, including its objectives, methodology and experimental results.

Aerodynamic techniques to mitigate the 3D loss in the power coefficient of vertical axis wind turbines

The three-dimensional tip loss effect is a critical phenomenon affecting the performance of vertical-axis wind turbines. The vortices on the blades become more complex with the turbine rotation, most notable at the tips, leading to three-dimensional aerodynamic losses and decreasing the turbine power coefficient. Therefore, mitigating the aerodynamic losses at the tips could improve the technological development of these devices. However, the numerical methods to analyze the tip vortices in VAWTs have a high computational cost, and experimental data to verify them is limited. In this study, three passive flow control techniques that mitigate the three-dimensional effects of a vertical axis wind turbine Darrieus H-type have been investigated experimentally in a wind tunnel to quantify their impact on the power coefficient and validate the theoretical results found in the literature. The tested passive flow control aerodynamic designs of the blade tips consist of leading-edge serration, anhedral, and endplate techniques. The results of this work include the experimental power coefficient curves as a function of the tip speed ratio for a two-blade VAWT model without any modification and with the three passive control techniques. The experimental process characterizes the VAWT techniques in a range of Tip Speed Ratios between 0.37 and 3.1. Our results indicate that the leading-edge serration, anhedral, and endplate techniques effectively mitigate the three-dimensional losses, increasing the power coefficient by 7.1%, 14.3%, and 25%, respectively, compared to the reference model. The endplate model exhibited the best Cp improvement. However, it could cause the highest bending on the blade tips of the three tested techniques.

Vertical-axis turbine performance enhancement with physics-informed blade pitch control. Basic principles and proof of concept with high-fidelity numerical simulation

In this study, we developed active physics-informed turbine blade pitch control methods to conquer the inconsistent energy harvesting efficiency challenges encountered by the vertical-axis turbines (VATs) technology. Specifically, individual turbine blades were pitched by actuators following commands from the physics-informed controllers, and the turbine performance improvements as a result of the blade pitch control mechanism and the associated flow physics were studied. The aim of the blade pitch control was to maintain constant effective angles of attack (AoAs) experienced by turbine blades through active blade pitch, and the constant AoA function was designed to facilitate control mechanism implementation into real-world VATs. To gain in-depth understanding of the capability of the control, flow physics was studied for different constant AoA control strategies across a wide range of tip speed ratios and wind speeds and was compared with that from the corresponding baselines without control, and that from the sinusoidal AoA control strategy. The comparison between the turbine performance with constant AoA control and that without control showed a consistent increase in the time-averaged net power coefficient, a measure of energy harvesting efficiency taking out of the actuator loss, ranging from 27.4% to 704.0% across a wide spread of wind speeds. The superior turbine performance with constant AoA control was largely attributed to blade dynamic stall management during the blade upstream and downstream cycles and the transition between the two cycles.

Performance enhancement of savonius hydrokinetic turbine using split airfoil blade: A numerical investigation

There is a concerted global effort to advance technology in the field of renewable energy sources due to the escalating energy crisis and escalating environmental pollution. One promising avenue for small-scale power generation is hydrokinetic technology. Among the various hydrokinetic turbines, the Savonius Hydrokinetic Turbine (SHT) stands out due to its specific advantages, but it has faced challenges in terms of performance. To address this, a novel blade design for the SHT has been developed, aiming to enhance its performance. This new turbine is referred to as the Split Airfoil Savonius Hydrokinetic Turbine (SASHT). To evaluate and compare the performance of both the conventional SHT and the newly developed SASHT, a Computational Fluid Dynamics (CFD) analysis has been conducted. This analysis encompasses a range of Tip Speed Ratios (TSR) from 0.7 to 1.2, with an inlet velocity of 0.8 m/s. The results reveal that the SASHT demonstrates a notable improvement, with a maximum Coefficient of Power that is 17% higher than that of the conventional semi-circular bladed SHT. This research offers valuable insights into the flow physics and performance parameters of these hydrokinetic turbines, showcasing the potential for more efficient and sustainable energy generation.

Evolving a Novel Blade Shape of a Savonius Wind Rotor Using an Optimization Technique Coupled With Numerical Simulations and Wind Tunnel Tests

Abstract The global adoption of Savonius wind rotors as an eco-friendly means of small-scale power production is on the rise. However, their suboptimal performance remains a significant challenge due to the generation of higher unproductive torque. This paper aims to address this issue by obtaining an optimal blade profile considering the power coefficient (CP) as an output function using optimization techniques. The objective function includes the overlap ratio, intermediate points on the curve, inlet velocity, and tip speed ratio (TSR) as the optimization geometric parameters. To achieve this, the simplex search method and the non-dominated sorting genetic algorithm II are opted to develop the blade profile. The blade profile is developed using a natural cubic spline curve with fixed end points and variable intermediate points along with other parameters. The computational analysis is done using ansys fluent software with shear stress transport k−ω turbulence model. The solver setup employs the finite volume method to simulate the transient 2D flow around the blade profile. A direct comparison is made between the optimized blade profile and the conventional semicircular one over a range of TSRs. The results clearly indicate the superior performance of the former, exhibiting a higher CPmax by 23% compared to the conventional one at TSR = 0.8. Finally, experiments have been conducted in a wind tunnel to find the practical feasibility of the optimized blade profile generated through the simplex search method.

Numerical Investigation of Lucid Spherical Cross-Axis Flow Turbine with Asymmetric Airfoil Sections and the Effect of Different Parameters of Blades on Its Performance

The numerical investigation has been performed on the cross-axis-flow lucid spherical turbine. This type of cross-axis flow turbine generates moments through the forces acting on its blade cross-sections. To evaluate its power and performance, a three-dimensional simulation procedure was performed. The experimental results of Bachant and Wosnik have been used to verify the numerical predictions. The spherical lucid model turbine which they examined had 4 blades with NACA 0020 section and 16cm chord length. Drag and power coefficients were used to compare the data for the water inlet velocity 1m/s and different non-dimensional tip-speed-ratio (inlet velocity / linear rotating velocity of the blade). This paper has selected two airfoil sections, NACA 2412 and NACA 64(3)418, to design the turbine blades. The influence of four effective blade parameters, inclusive of profile section type, chord length, number of blades, and blade twist angles, on turbine performance over a wide range of tip speed ratios, is investigated. It can deduce that the power coefficient has increased up to 22% for NACA 2412 compared to the experimental test. Also, the three-bladed turbine possesses the best results among all models. For this model, the power coefficient increased by 12% and 71% for NACA 2412 and NACA 64(3)418 sections, respectively. The twist of the blades increases the power coefficient by 19% and 31% for NACA 2412 and NACA 64(3)418 sections inside the channel respectively. Increasing the blade chord length causes to increase in power coefficient of up to 12% for NACA 2412 section compared to the experimental test.

Calibration method of the k-ω SST turbulence model for wind turbine performance prediction near stall condition

The present study intends to enhance the accuracy of the k–ω SST turbulence model for numerical wind turbine simulation in stall condition. In order to achieve this purpose a calibration approach is proposed, and is applied to NREL S826 NTNU wind rotor. This method consists in adjusting the two turbulence model coefficients: a1 and β*, which are found to be 0.8 and 0.45 respectively. Then the calculated power and thrust coefficients are compared to the experimental results. The power coefficient results revealed that the simulation relative error at the range of tip speed ratio between 3 to 6 where light stall occurs, is reduced from 17.89 % to 4.58 % by application of calibration. The effects of calibration on flow behaviour are implemented thereafter, by analysing pressure, and skin friction coefficients distribution along the blade. The limiting streamlines on the blade suction side are examined for more flow behaviour understanding. The effects on turbulent kinetic energy around the blade are also highlighted. The main important conclusions that can be made is that calibration reduce the separation zone on the blade suction side, and limits the vortex shedding strength, leading to improve the rotor efficiency and hence to improve the model accuracy.

Design approach of thrust-matched rotor for basin model tests of floating straight-bladed vertical axis wind turbines

Rotor redesign approaches have been widely proposed to solve the thrust mismatch issue caused by scaling effects for basin model tests of horizontal axis floating wind turbines (FWTs). However, limited basin model tests utilized the thrust-matched rotor (TMR) to accurately evaluate the aerodynamic loads applying to the vertical axis FWTs. This paper described the detailed design approach of the TMR of floating straight-bladed vertical axis wind turbines (VAWTs) with a rated power of 5.3 MW. First, the AG455 airfoil was selected to replace the NACA0018 airfoil. AG455 airfoil can show a larger lift coefficient and a smaller drag coefficient at low Reynolds number. On this basis, the load distribution match algorithm was used to assign the blade pitch angle and chord length at each section of the blade. This method takes the spanwise load and load change rate of model-scaled blade and full-scaled blade as the constraint conditions. By adopting this method, the rotor thrust can be tailored to match the prototype values across a wide range of tip speed ratios. This design approach proves advantageous in assessing the aerodynamic performance of VAWTs under varying inflow wind speeds and unsteady wind conditions. The redesigned TMR model under low Reynolds number can meet Froude similarity criterion, which is helpful to improve the accuracy of vertical axis FWT model tests in the wave basin.

Design modification and performance prediction of ellipsoid cross-flow hydrokinetic turbine

In this study, an ellipsoid-shaped cross-flow hydrokinetic (ECFHKT) has been selected for the study. The performance of the ECFHKT was investigated for different design parameters, namely the number of blades, blade angle and blade length. The performance of ECFHKT was evaluated in terms of coefficient of torque (Ct) and coefficient of power (Cp) with respect to different tip speed ratios (TSR) by considering different flow velocities in the range of 0.5 m/s to 3.0 m/s, experimentally and numerically. Further, the Flow behavior across the ECFHKT was analyzed and discussed through pressure contour, velocity contour and velocity vector. It was found that design parameters play a vital role in enhancing the performance of the rotor and self-starting capabilities. For this analysis, the maximum Ct and Cp were obtained as 1.08 and 0.267, respectively. Further, It was observed that the ECFHKT performed well both in low and high flow conditions within a narrow range of tip speed ratio.

Design and performance investigation of a triple blade dual stage Savonius-alike hydrokinetic turbine from low flow stream reserves

ABSTRACT A trending technology that is being employed to generate hydro energy from low-flow stream reserves is the Savonius-alike hydrokinetic turbine (SAHT). Clearance between the stages of a dual-stage two-bladed SAHT was found to improve its performance at low flow speeds; however, the impact of clearance on the triple-bladed configuration of SAHT was not studied earlier. In this paper, a triple blade dual stage configuration of SAHT is designed, and its performance is investigated in a water flume under various stage clearances (0,5,10,15 and 20 mm), low flow speeds (0.45,0.55 and 0.65 m/s) and different brake loads. Detailed turbine performance under different design and off-design conditions are investigated to obtain meaningful performance insights. The findings show that torque production by the turbine increases with the increase of brake load, with maximum hydrodynamic torque generated at the highest brake load. The highest coefficient of performance and torque of 0.071 and 0.261 are obtained at a stage clearance of 5 mm, tip speed ratio of 0.273, and free-stream flow speed of 0.55 m/s. The present SAHT under design condition has improved performance compared to a dual blade dual stage SAHT exhibiting a wider tip speed ratio range for its application in low flow stream reserves. Further, this turbine may also be recommended for torque generation to work as a motor in a flow speed condition less than 0.5 m/s. The novelty of this work is the application of an additional flow control measure in the form of flow-through clearance to negotiate vertical water thrust through the clearance and exert additional pressure on the advancing blades of the SAHT in the upper stage.

Experimental techniques for evaluating the performance of high-blockage cross-flow turbine arrays

Cross-flow turbines show great promise for extracting power from water currents since their rectangular projected area allows them to achieve high blockage. As a turbine’s blockage ratio—the ratio of the rotor projected area to the channel cross-sectional area—increases, its efficiency and structural loading increase since both kinetic and potential energy in the freestream are converted to mechanical power. For an array of turbines deployed in a river or tidal channel, the array blockage ratio will vary due to daily or seasonal fluctuations in the water level, as well as when individual turbines are deactivated for maintenance. Consequently, understanding how the performance characteristics of the array change as confinement is varied is of practical interest.
 Here, we characterize the performance of a laboratory-scale two-turbine array at various levels of confinement in a recirculating water channel. The array blockage ratio was varied from 30% to 60%—the upper end of what might be realizable in a natural channel. Two experimental approaches for varying the blockage were considered: 1) altering the channel cross-sectional area via a change in water depth, and 2) altering the array projected area by changing the blade span. Across all tested blockage ratios, the nominal chord-based Reynolds number (4.0 x 104) and nominal depth-based Froude number (0.22) were held constant, and the submergence-based Froude number was minimized to avoid ventilation of the turbine rotors at the upper end of the tested blockages. At each blockage ratio, the turbine performance was evaluated across a range of tip-speed ratios under a counter-rotating, phase-locked control scheme, wherein the turbines rotate at the same, constant speed but in opposite directions, with a constant angular phase offset, Δθ, between them. We focus this work on Δθ = 0°, an operating case in which the lateral forces and reaction torques for a pair of turbines are equal and opposite, which is advantageous for support structure design.
 As the array blockage ratio is increased, we observe significant increases in the array performance and thrust coefficients, as well as an increase in the range of tip-speed ratios over which the array produces power. For the highest confinements, peak power coefficients exceed unity and thrust coefficients are substantially higher than in conventional array designs. We observe disparities between the power and thrust coefficients for arrays with the same blockage ratio, but different blade spans. We attribute the higher performance for longer blade spans to differences in the relative magnitude of parasitic support structure losses between the two rotors, as well as free surface effects. Further, we explore the effectiveness of techniques for accounting for these performance differences through the estimation of blade-level performance.
 Overall, our results provide a solid foundation for understanding how the performance of cross-flow turbine arrays change as a function of the array blockage ratio, and highlight considerations for the design of cross-flow turbine experiments.

Power performance and self-starting features of H-rotor and helical vertical axis wind turbines with different airfoils in turbulence

Wind tunnel tests were conducted to systematically assess the aerodynamic performance of both H-rotor and helical vertical axis wind turbines (VAWTs) in smooth and turbulent flows. The effects of airfoil section and pitch angle β on the power and self-starting performance were examined for both types of turbines. The helical turbine had a wider operating range of tip speed ratios (TSR λ) and much lower power performance than its H-rotor counterpart. This phenomenon was attributed to the flow deflection of helical blades due to their three-dimensional features, as well as that dynamic stall of a helical blade would not occur simultaneously for all blade elements. The helical turbine did not exhibit notably improved self-starting performance despite of the high manufacturing cost. Moreover, the start-up process was analyzed by using the static torque coefficient CT of both single-bladed and three-bladed turbines. It was found that turbulence intensity exercised a significant impact on CT. Turbulence would cause serious fatigue issues for H-rotor turbines and change the driving mechanism of helical turbines though it enhanced the self-starting performance. Recommendations were finally provided for the design of VAWTs in built environments.

Aerodynamic performance improvements for a Savonius turbine above a forward-facing step via inclined solar panel: A computational study

The transformation of urban energy structure is an urgent problem to be solved in sustainable construction. To fully exploit and utilise renewable energy, this study proposes a novel wind–solar energy hybrid harvesting system that combines an inclined solar panel and a Savonius wind turbine installed on a building roof. The effects of the tilt angle of the solar panels and tip speed ratios (TSRs) on the aerodynamic performance of the turbine were investigated using high-fidelity large-eddy simulations (LES) at a Reynolds number of Re = 4.45 × 105. Five tilt angles in the range of 30°–60° were tested, and the range of TSR was 0.2–1.6. For comparison, two other installation cases were also studied, including the case of a Savonius turbine alone and the case of a single Savonius turbine placed at a fixed height position on a forward-facing step. The results showed that the power coefficient of the Savonius turbine increased and then decreased with tilt angle or TSR. When TSR = 1, the power coefficient in the system reached a maximum value of Cpmax = 0.638 at a tilt angle of 45°, 254.4% and 11.7% higher than those of the other two installation cases, respectively. The flow-field comparison results reveal why the proposed system can improve the energy harvesting efficiency. The presence of a solar panel with a suitable tilt angle increases the velocity and volume of the airflow hitting the advancing blade, creating a greater pressure difference around the blades that is caused mainly by the decrease in the low pressure on the concave surface of the advancing blade. Thus, the net torque applied to the turbine blades increases, which is conducive to driving turbine rotation. The proposed system is beneficial for improving the aerodynamic performance of Savonius turbines and the utilisation of renewable energy in urban areas.

Aerodynamic analysis of a 2-stage elliptical-bladed Savonius wind rotor: Numerical simulation and experimental validation

ABSTRACT The Savonius rotor is a type of vertical-axis wind turbine that utilizes drag to generate power. Its design simplicity and ability to self-start at low wind speeds make it an attractive option for small-scale wind energy generation. Previous research has focused on optimizing the geometric configuration of a 1-stage, 2-bladed rotor with semicircular blade profiles to improve its performance and mitigate negative torque. However, limited research has been conducted on 2-stage, 2-bladed Savonius rotors with elliptical blade profiles. The present investigation aims to fill this research gap by evaluating the aerodynamic characteristics of a 2-stage, 2-bladed Savonius rotor with elliptical profiles. 3D unsteady simulations using the SST k-ω turbulence model in ANSYS Fluent are conducted to evaluate the performance coefficients over a range of tip speed ratios. The numerical results are validated through wind tunnel experiments. The results show that the CPmax (maximum power coefficient) for the 1-stage rotor is 0.19 and 0.12 for numerical and experimental analyses, respectively. For the 2-stage rotor, the CPmax is 0.21 and 0.17 for numerical and experimental analyses, respectively. These findings suggest that the 2-stage rotor with elliptical profiles has the potential to efficiently harness wind energy.